Discussion about the Korg PolySix synthesizer

Hello guys, 

I've just started to work on tunning the voices and i realised my opto coupler is dead. 

So i read through the topics and learned that VTL5C3 would be the sollution. However i only got VTL5C2 which has only two pin on the photoresistor side, with a connection in the middle of the resistor which is connected to R93 which is said requires some changes. 

So what is that middle pin required for ? How can a 2 pin photocoupler be used if possible at all ?

Any thoughts? 

Thanks
Razvan